This invention relates to aromatic polyesters useful in the production of films and fibers. More particularly, it relates to aromatic polyesters exhibiting desirable low-melting and melt-processable characteristics.
The production of polyesters, including aromatic polyesters, by the polycondensation of dicarboxylic acids (or the corresponding acyl halides) and polyhydric alcohols has been well known. For example, the production of polyesters is described in U.S. Pat. No. 3,008,929 (issued Nov. 14, 1961 to E. A. Wielicki); in U.S. Pat. No. 3,786,022 (issued Jan. 15, 1974 to N. Hata et al.); in U.S. Pat. No. 4,066,620 (issued Jan. 3, 1978 to J. J. Kleinschuster); in U.S. Pat. No. 4,083,829 (issued Apr. 11, 1978 to G. W. Calundann et al.); in U.S. Pat. No. 4,288,588 (issued Sept. 8, 1981 to J. A. Donohue); and in U.S. Pat. No. 4,433,132 (issued Feb. 21, 1984 to H. G. Rogers et al.). In general, it is well recognized that the mechanical and physical properties of polymeric films and fibers will depend upon the chemical structure of the polymers from which they are prepared and that such properties can be materially influenced by such molecular factors as chain stiffness, intermolecular forces, orientation and crystallinity. Accordingly, there has been considerable interest in the development of polyesters having particular structural or molecular configurations for the realization of one or more particular properties suited to a desired application.
In the production of polyester films and fibers, it will generally be advantageous to prepare such films and fibers either from a solution of the polyester in a common and readily available solvent or from a processable melt of the polyester material. Frequently, and particularly in the case of wholly aromatic polyesters, the polyester material may be substantially insoluble; and when the polyester can be suitably dissolved and processed from a solvent material, film and fiber production will require the handling and recovery of the solvent material. Moreover, melt processability is frequently hampered by the tendency of the polyester materials to be melt processable only at elevated temperatures which, in some instances, may approach the onset of thermal degradation. It will be appreciated that the characteristic and advantageous properties of a polyester suited to a particular application will be more readily realized where the polyester material exhibits low-melting behavior and can be melt processed into films and fibers at relatively low processing temperatures.